Locking compound rotary actuator

ABSTRACT

The subject matter of this specification can be embodied in, among other things, a rotary lock assembly that includes a first epicyclic gear assembly having a first sun gear assembly, a first ring gear assembly, and a first planet gear assembly mechanically engaged to the first sun gear assembly and the first ring gear assembly, and a second epicyclic gear assembly having a second sun gear assembly configured to be rotated by the first ring gear assembly, a second ring gear assembly, and a second planet gear assembly mechanically engaged to the second sun gear assembly and the second ring gear assembly.

TECHNICAL FIELD

This instant specification relates to rotary-to-linear motion conversiondevices for use with aircraft cascade reverser actuators.

BACKGROUND

Conventional linear actuators have output rams that may be driven by amotor or with pneumatic or hydraulic pressure. The actuator may have alock mechanism to retain the output in a fixed position. Known lockmechanisms, such as taught by Tootle in U.S. Pat. No. 4,463,661, engagean actuator synchronization system, and therefore provide only indirectlocking to the output ram. Direct locking mechanisms that employ alinear actuator have been developed and typically include a multi-piecehousing with increased size and mass. Such actuators include tine locks,an example of which is disclosed by Carlin in U.S. Pat. No. 5,267,760.While some tine lock arrangements may allow for a single-piece housingactuator, they have the disadvantage of using a flexing lock elementwith consequential fatigue considerations. Locking actuators can beoperated by a rotary source rather than hydraulically or pneumatically.Present rotary source operated actuators, such as disclosed by Grimm inU.S. Pat. No. 4,603,594, have the disadvantage of requiring anelectrically operated solenoid mechanism (or other mechanical inputseparate from the rotary source) to unlock the actuator lock beforemotion of the ram can commence. Ball lock mechanisms such as taught bySue in U.S. Pat. No. 4,703,683, Deutch in U.S. Pat. No. 4,240,332 andDella Rocca in U.S. Pat. No. 4,742,758 have the disadvantage of a lowexternal load carrying capability of the ram, because of the pointcontact stresses imposed on the lock balls. Linear motion lock sleeveand key arrangements, such as disclosed by Kopecek (the inventor of thepresent disclosure) in UK patent GB2435877, include a rotary-to-linearmotion conversion mechanism for the lock sleeve and complexityassociated therewith. Rotary lock sleeve and key arrangements have alsobeen disclosed by Kopecek in U.S. Pat. No. 8,715,132. Accordingly, itwould be desirable to provide a linear actuator arrangement thatovercomes at least some of the problems identified above.

SUMMARY

In general, this document describes rotary-to-linear motion conversiondevices. More particularly, this document describes rotary-to-linearmotion conversion devices for use with aircraft cascade reverseractuators.

In an example embodiment, a rotary lock assembly includes a firstepicyclic gear assembly having a first sun gear assembly, a first ringgear assembly, and a first planet gear assembly mechanically engaged tothe first sun gear assembly and the first ring gear assembly, and asecond epicyclic gear assembly having a second sun gear assemblyconfigured to be rotated by the first ring gear assembly, a second ringgear assembly, and a second planet gear assembly mechanically engaged tothe second sun gear assembly and the second ring gear assembly.

Various embodiments can include some, all, or none of the followingfeatures. The rotary lock assembly can also include a lock keyconfigured for radial displacement between a first lock keyconfiguration and a second lock key configuration, and a lock rotorconfigured to be rotated by the second planet gear assembly between afirst rotor configuration in which radial displacement of the lock keyfrom the first lock key configuration to the second lock keyconfiguration is prevented, and a second rotor configuration in whichradial displacement of the lock key from the first lock keyconfiguration to the second lock key configuration is permitted. Therotary lock assembly can also include a first lock rotor stop configuredto prevent rotation of the lock rotor in a first direction at the firstrotor configuration, and a second lock stop configured to preventrotation of the lock rotor in a second direction at the second rotorconfiguration. The rotary lock assembly can also include a lock keyretainer configured to be moved linearly between a first lock keyretainer configuration in which radial displacement of the lock key fromthe second lock key configuration to the first lock key configuration isprevented, and a second lock key retainer configuration in which radialdisplacement of the lock key from the second lock key configuration tothe first lock key configuration is permitted. The rotary lock assemblycan also include a linear output assembly configured for axial movementrelative to radial movement of the lock key, and having an outer surfacedefining a groove between a first axial groove face and a second axialgroove face, and configured to receive the lock key in the first lockkey configuration and be prevented from moving linearly based onmechanical interference between the lock key and at least one of thefirst axial groove face and the second axial groove face. The rotarylock assembly can also include a screw lead engaged to the first planetgear assembly and responsive to revolution of the first planet gearassembly, and a nut engaged with the screw lead and axially movablealong the screw lead in response to rotation of the screw lead. Therotary lock assembly can also include a housing engaged to the secondring gear assembly, and an input shaft coupled to the first sun gearassembly and rotatable relative to the housing. The second ring gearassembly can be configured to remain fixed relative to motion of thesecond sun gear assembly.

In an example implementation, a method of locking a linear actuatorincludes receiving torque at a first sun gear of a first epicyclic gearassembly, transmitting torque from the first sun gear to a first ringgear of the first epicyclic gear assembly through a first planet gearassembly of the first epicyclic gear assembly, transmitting torque fromthe first planet gear assembly to a screw, urging movement of a linearoutput member through a nut configured for linear motion based onrotation of the screw, transmitting torque from the first ring gear to asecond sun gear of a second epicyclic gear assembly, and transmittingtorque from the second sun gear to a second planet gear engaged betweenthe second sun gear and a second ring gear.

Various implementations can include some, all, or none of the followingfeatures. The method can also include urging radial displacement of alock key from a first lock key configuration to a second lock keyconfiguration based on linear movement of the linear output member. Themethod can also include contacting, based on movement of the linearactuator, the lock key with an axial groove face of a groove defined inthe linear output member and configured to receive the lock key in thefirst lock key configuration, preventing linear movement of the linearoutput member based on interference between the lock key and the axialgroove face, preventing rotation the screw based on the prevented linearmovement of the linear output member, preventing rotation of the firstplanet gear assembly based on the prevented rotation of the screw, andtransmitting substantially all torque received at the first sun gear tothe first ring gear. The method can also include transmitting torquefrom the second planet gear to a lock rotor, and rotating the lock rotorfrom a first lock rotor configuration to a second lock rotorconfiguration. The first lock rotor configuration can be a firstrotational position defined by a first lock rotor end stop configured tointerfere with rotation of the lock rotor in a first direction, and thesecond lock rotor configuration is a second rotational position definedby a second lock rotor end stop configured to interfere with rotation ofthe lock rotor in a second direction opposite the first direction. Thelock rotor can be configured to prevent radial displacement of a lockkey from a first key configuration to a second key configuration in thefirst lock rotor configuration, and is configured to permit radialdisplacement of the lock key from the first key configuration to thesecond key configuration in the second lock rotor configuration.

In another example embodiment, a linear actuator includes a housing, arotary input member rotatably moveable relative to the housing, a linearoutput member axially movable between a first output position relativethe housing, and a second output position relative to the housing, and arotary lock assembly disposed within the housing and constrained fromaxial motion, the rotary lock assembly having a first epicyclic gearassembly that includes a first sun gear assembly, a first ring gearassembly, and a first planet gear assembly mechanically engaged to thefirst sun gear assembly and the first ring gear assembly, and a secondepicyclic gear assembly that includes a second sun gear assemblyconfigured to be rotated by the first ring gear assembly, a second ringgear assembly, and a second planet gear assembly mechanically engaged tothe second sun gear assembly and the second ring gear assembly.

Various embodiments can include some, all, or none of the followingfeatures. The rotary lock assembly can also include a lock keyconfigured for radial displacement between a first lock keyconfiguration and a second lock key configuration, and a lock rotorconfigured to be rotated by the second planet gear assembly between afirst rotor configuration in which radial displacement of the lock keyfrom the first lock key configuration to the second lock keyconfiguration is prevented, and a second rotor configuration in whichradial displacement of the lock key from the first lock keyconfiguration to the second lock key configuration is permitted. Therotary lock assembly can also include a first lock rotor stop configuredto prevent rotation of the lock rotor in a first direction at the firstrotor configuration, and a second lock stop configured to preventrotation of the lock rotor in a second direction at the second rotorconfiguration. The rotary lock assembly can also include a lock keyretainer configured to be moved linearly between a first lock keyretainer configuration in which radial displacement of the lock key fromthe second lock key configuration to the first lock key configuration isprevented, and a second lock key retainer configuration in which radialdisplacement of the lock key from the second lock key configuration tothe first lock key configuration is permitted. The rotary lock assemblycan also include a linear output assembly configured for axial movementrelative to radial movement of the lock key, and having an outer surfacedefining a groove between a first axial groove face and a second axialgroove face, and configured to receive the lock key in the first lockkey configuration and be prevented from moving linearly based onmechanical interference between the lock key and at least one of thefirst axial groove face and the second axial groove face. The rotarylock assembly can also include a screw lead engaged to the first planetgear assembly and responsive to revolution of the first planet gearassembly, and a nut engaged with the screw lead and axially movablealong the screw lead in response to rotation of the screw lead. Therotary lock assembly can also include a housing engaged to the secondring gear assembly, and an input shaft coupled to the first sun gearassembly and rotatable relative to the housing. The second ring gearassembly can be configured to remain fixed relative to motion of thesecond sun gear assembly.

The systems and techniques described here may provide one or more of thefollowing advantages. First, a system can lock linear actuators againstunintended extension. Second they system can provide more reliableunlocking operations, especially under conditions of high mechanicalloads on the linear actuators. Third, the system can automaticallyprovide the additional torque needed to perform the unlocking. Fourth,the system can provide the additional torque without additional controlor power inputs.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a front perspective view of an example linear actuator.

FIGS. 2 and 3 show cross section views of an example locking rotaryactuator mechanism in a locked configuration.

FIG. 4 shows a cross section view of the example locking rotary actuatormechanism in a partly unlocked configuration.

FIGS. 5 and 6 show cross section views of the example locking rotaryactuator mechanism in an unlocked configuration.

FIGS. 7A and 7B show a front perspective and a cross section view of anexample lock key.

FIG. 8 shows a cross section view of the example locking rotary actuatormechanism.

FIG. 9 shows another cross section view of the example locking rotaryactuator mechanism.

FIG. 10 shows another cross section view of the example locking rotaryactuator mechanism.

FIG. 11 shows another cross section view of the example linear actuatorof FIG. 1 .

FIG. 12 shows a flow diagram of an example process for operating alinear actuator.

DETAILED DESCRIPTION

This document describes systems and techniques for providingrotary-to-linear motion with an actuator device that can be locked toprevent unintentional movement. Some prior locking designs are limitedin the amount of tension load that may be applied to the actuator ramwhile still allowing lock keys to unlock. The designs described in thisdocument provide a capability to unlock the actuator under thehigh-tension loads that can be generated by the latest technology thrustreversers. As will be discussed in more detail below, the actuatorincludes features that automatically redirect input torque when needed,in order to overcome binding or lock components under high input forces.In general, the rotary-to-linear conversion function of the actuator isachieved with a multi-stage planetary gearbox, in which one stage drivesthe rotary-to-linear conversion, and resistance to that conversiondrives a second stage that performs unlocking actions. The second stageis gear-reduced to provide increased torque to perform the unlocking,which can be helpful in situations when high linear forces can cause thelocking components to bind or otherwise become difficult to unlock.

FIG. 1 illustrates a front perspective view of an example linearactuator 100 incorporating aspects of the disclosed embodiments. Theactuator 100 has an outer housing 104 and an output ram 108 (e.g., alinear output assembly). The output ram 108, which is capable of axialmovement or motion (depicted by direction arrow 110) into and out of thehousing 104, such as from a retracted output position as shown in FIG. 1. In some embodiments, the linear actuator 100 can be part of a thrustreverser actuation system (TRAS). As a non-limiting example, the ram 108may be attached to a door, panel, or engine thrust reverser, while thehousing 104 is attached to a frame of a larger object, such as, but notlimited to, an airplane. Movement of the ram 108 thereby determines theposition of the door, panel, or thrust reverser, or other attachingsurface.

Within the housing 104, an actuator (not shown) drives the extension andretraction of the output ram 108 based on rotational energy receivedfrom a synchronization shaft (not shown) connected to the actuatorthrough an aperture 122 a and/or 122 b. This actuator will be describedin more detail in the descriptions of FIGS. 2-6 . In some embodiments,the linear actuator 100 can also include a sensor configured to providepositional signals or information that is representative of the linearoutput position (e.g., extension or retraction) of the output ram 108.

When the output ram 108 is retracted into the housing 104, a lockingrotary actuator mechanism 120 may be locked to prevent inadvertent orunintended extension of the ram 108 from the housing 104. The lockingrotary actuator mechanism 120 for the linear actuator 100 is discussedin more detail below.

FIGS. 2 and 3 show cross section views of an example locking rotaryactuator mechanism 200 in a locked configuration. In some embodiments,the locking rotary actuator mechanism 200 can be the example lockingrotary actuator mechanism 120 of FIG. 1 .

The locking rotary actuator mechanism 200 includes a housing 202, rotaryinput shaft member 204, and a linear output assembly 206. Rotation ofthe rotary input shaft member 204 (e.g., by a synchronization shaft, bya direct-drive motor) urges linear motion of the linear output member106 through an epicyclic gear assembly 210, a rotary lock assembly 260,and a rotary-to-linear motion conversion assembly 280. Therotary-to-linear motion conversion assembly 280 includes a screw lead282 that is rotated by the epicyclic gear assembly 210, and a nut 284that is affixed to the linear output assembly 206 and is driven linearlyas the screw lead 282 rotates.

The rotary lock assembly 260 includes a collection of lock keys 262 thatare configured for radial displacement and to engage with a groove 264defined in a radially outer surface of the linear output assembly 206.The groove 264 includes an axial groove face 266 a and an axial grooveface 266 b. The axial groove face 266 b is configured with a bevel thatis complimentary to a bevel 263 of the lock key 262. In someembodiments, the bevel 263 is angled typically about 25 degrees from theradially outward direction. When locked, the lock keys 262 prevent thelinear output assembly 206 from extending by contacting the axial grooveface 266 b. The lock keys 262 are prevented from moving radially out ofthe locked position by a lock rotor 270. The lock rotor 270 can bepartly rotated to selectively prevent and permit radial movement of thelock keys 262. The lock rotor 270 is discussed in more detail in thedescription of FIG. 11 .

The epicyclic gear assembly 210 includes an epicyclic gear subassembly212 a and an epicyclic gear subassembly 212 b. The screw lead 282 isrotated by the rotary input shaft member 204 thought the epicyclic gearsubassembly 212 a. The lock rotor 270 is rotated by the rotary inputshaft member 204 through the epicyclic gear subassembly 212 b.

The epicyclic gear subassembly 212 a includes a sun gear assembly 220, aring gear assembly 222, and a planet gear assembly 224. The epicyclicgear subassembly includes a sun gear assembly 230, a ring gear assembly232, and a planet gear assembly 234. The ring gear assembly 232 isaffixed (e.g., grounded) to the housing 202 or otherwise prevented fromrotating relative to the rotary input shaft member 204, the screw lead282, and the other components of the epicyclic gear assembly 210. Thesun gear assembly 230 is affixed to or otherwise configured to be drivenby rotation of the ring gear assembly 222. A planet carrier 225 connectsthe planet gear assembly 224 to the screw lead 282 such that rotation ofthe planet gear assembly 224 can urge rotation of the screw lead 282. Aplanet carrier 235 connects the planet gear assembly 234 to the lockrotor 270 such that rotation of the planet gear assembly 224 can urgerotation of the lock rotor 270.

The locking rotary actuator mechanism 200 uses a lost motion mechanismincorporating the epicyclic gear assembly 210 that operates as a stargear (e.g., grounded planet gear assembly 224 where the sun gearassembly 220 drives the ring gear assembly 222) during the unlockingprocess of the lock keys 262, and then operates as a planetary gear(e.g., grounded ring gear assembly 222 where the sun gear assembly 220drives the planet gear assembly 224). In some implementations, thisarrangement can provide force for unlocking of the lock as long astension loads upon the output ram 108 are not too great. This is becausetension loads on the piston are reacted into a radially outward force onthe lock keys 262 by the bevel 263 and the axial groove face 266 b. Thetension load on the piston therefore results in an increased frictionalforce between the lock key 262 and an inner face of the lock rotor 270.This friction force opposes the unlocking torque on the ring gearassembly 222 when the epicyclic gear subassembly 212 a is operating instar (unlocking) mode.

Referring now to FIG. 3 , the example locking rotary actuator mechanism200 is shown in an initial state of unlocking. In the illustratedexample, a high tension exists on the linear output assembly 206. Hightension loads imposed on the linear output assembly 206 (e.g., byadvanced technology thrust reversers) during the unlocking process cancreate a frictional force between the lock keys 262 and the lock rotor270 that is high enough to prevent rotation of the lock rotor 270 duringthe unlocking process. Without the help of additional mechanical forceprovided by the epicyclic gear subassembly 212 b, such frictional forcescould prevent unlocking in some circumstances.

With the linear output assembly 206 locked, the rotary-to-linear motionconversion assembly 280 is substantially prevented from operating andthe screw lead 282 substantially prevented from rotating. As such, theplanet carrier 225 and the planet gear assembly 224 are alsosubstantially prevented from moving. As such, the carrier 225 of planetgear assembly 224 is substantially grounded.

The rotary input shaft member 204 is rotated, which urges rotation ofthe sun gear assembly 220. Substantially all of the torque provided bythe sun gear assembly 220 is transmitted through the planet gearassembly 224 (e.g., which is currently grounded) to the ring gearassembly 222. The ring gear assembly 222 rotates, urging rotation of thesun gear assembly 230.

Since the ring gear assembly 232 is grounded to the housing 202,rotation of the sun gear assembly 230 urges rotation of the planet gearassembly 234. Rotation of the planet gear assembly 234 is transmittedalong the planet carrier 235 to urge rotation of the lock rotor 270. Inthe illustrated example, substantially all of the torque provided at therotary input shaft member 204 is transmitted to the lock rotor 270, andthe epicyclic gear subassembly 212 b provides a gear reduction thatmultiplies the force that is available to overcome friction between thelock keys 262 and the lock rotor 270.

FIG. 4 shows a cross section view of the example locking rotary actuatormechanism 200 in a partly unlocked configuration. Once the frictionbetween the lock keys 262 and the lock rotor 270 has been overcome, thelock rotor 270 can begin to rotate such that the lock keys 262 arepermitted to move radially outward. With the lock keys 262 being able tomove, the linear output assembly 206 and the rotary-to-linear motionconversion assembly 280 are also able to start moving.

With the screw lead 282 able to rotate, the planet carrier 225 and theplanet gear assembly 224 are also able to start to rotate. At thisstage, a relatively small portion of the torque at the sun gear assembly220 is available for transfer through the planet gear assembly 224 andthe planet carrier 225 to start initial rotation of the screw lead 282and cause an initial extension movement of the linear output assembly206. Movement of the linear output assembly 206 causes mechanicalinterference between the axial groove face 266 b and the bevel 263,which urges radially outward movement of the lock keys 262.

Also visible in FIG. 4 is a lock key retainer 290 configured to be movedlinearly between a first lock key retainer configuration in which radialdisplacement of the lock keys 262 from the unlocked position to thelocked position is prevented, and a second lock key retainerconfiguration in which radial displacement of the lock key 262 from theunlocked position to the locked position is permitted. The lock keyretainer 290 includes a stationary portion 292 that is directly orindirectly affixed to the housing 202 to remain substantially unmovedrelative to movement of the linear output assembly 206. The lock keyretainer 290 also includes a moveable portion 294 that is configured tomove linearly relative to the stationary portion 292. The lock keyretainer 290 also includes a bias member 296 (e.g., a spring) that ispartly compressed between the stationary portion 292 and the moveableportion 294, to urge the moveable portion 294 into contact with thelinear output assembly 206. In the illustrated example, the lock keyretainer 290 is compressed and inactive, but the function of the lockkey retainer 290 will be discussed further in the description of FIG. 5.

FIGS. 5 and 6 show cross section views of the example locking rotaryactuator mechanism 200 in an unlocked configuration. The lock rotor 270is configured to rotate through a limited, predetermined range of angles(e.g., about 15 degrees) between a hard stop at a position correspondingto the locked configuration (e.g., in which the lock keys 262 are ableto fully escape the groove 264) and another hard stop at a positioncorresponding to a fully unlocked configuration (e.g., in which the lockkeys 262 are prevented from escaping the groove 264). The configurationof the lock rotor 270 is discussed in more detail in the description ofFIG. 11 .

In FIG. 5 , the lock rotor 270 is hard stopped at the position thatcorresponds to the unlocked configuration. The hard stop preventsfurther rotation of the lock rotor 270, substantially grounding the lockrotor 270 and preventing further rotation of the planet carrier 235, theplanet gear assembly 234, the sun gear assembly 230, and the ring gearassembly 222. With the ring gear assembly 222 effectively grounded,substantially all of the torque provided at the rotary input shaftmember 204 to be directed through the planet gear assembly 224 and theplanet carrier 225 to the screw lead 282 to urge extension of the linearoutput assembly 206. With the lock keys 262 being fully escaped from thegroove 264, the linear output assembly 206 is able to extend.

As the linear output assembly 206 extends its output position, the biasmember 296 expands between the stationary portion 292 and the moveableportion 294, urging the moveable portion 294 to follow the linear outputassembly 206 as it extends. The moveable portion 294 provides a radialface that substantially extends the radially outermost surface of thelinear output assembly 206. As the linear output assembly 206 extendsbeyond the axial output position location of the lock keys 262, themoveable portion 294 moves to provide a physical barrier that keeps thelock keys 262 in the radially extended, unlocked position.

In FIG. 6 , the linear output assembly 206 continues to extend while thelock keys 262 are maintained in their unlocked positions. Retraction ofthe linear output assembly 206 is performed by reversing the rotation ofthe rotary input shaft member 204, which brings the linear outputassembly 206 back into contact with the moveable portion 294 to urgecompression of the bias member 296 and allow the lock keys 262 to moveradially out of the unlocked position toward the locked configurationwithin the groove 264. Once the linear output assembly 206 is fullyretracted, the sun gear assembly 230 effectively becomes grounded, andtorque is directed toward rotation of the lock rotor 270 toward thelocked position. The lock rotor 270 is configured to urge the lock keys262 to move radially inward into the groove 264 and prevent them frombeing displaced radially (e.g., due to tension on the linear outputassembly 206).

FIGS. 7A and 7B show a front perspective and a cross section view of anexample lock key 700. In some embodiments, the lock key 700 can be theexample lock key 262 of FIGS. 2-6 . The lock key 700 has a front face702 and a rear face 704. The rear face 704 includes a bevel 706 (e.g.,angled about 25 degrees relative to the rear face). In some embodiments,the bevel 706 can be the bevel 263. In the locked configuration, thebevel 706 contacts the axial groove face 266 b to prevent extension ofthe linear output assembly 206.

The lock key 700 has bottom surface 710 that is configured to restagainst the linear output assembly 206 in the locked configuration andrest against the moveable portion 294 of the lock key retainer 290 inthe unlocked configuration. The bottom surface 710 includes bevels 712 aand 712 b that can guide radially inward movement of the lock key 700(e.g., moving into locking position within the groove 264).

The lock key 700 also has a crown 720 that is configured to contact thelock rotor 270. In the locked configuration, a top surface 722 of thecrown contacts an inner radius of the lock rotor 270 to retain the lockkey in the radially inward, locked configuration. In the unlockedconfiguration, the crown 720 extends into a corresponding, radiallyoutward recess in the lock rotor that can rotate into and out of radialalignment with the crown 720.

The crown 720 includes a radiused face 724 a and a radiused face 724 b.During locking, the lock rotor 270 rotates relative to the lock key 700,and the radiused faces 724 a-724 b act as ramps against thecircumferential ends of the lock rotor recesses to urge the lock key 700to move radially inward into the locked configuration.

FIGS. 8-11 depict an exemplary embodiment of a lock assembly 800. Insome embodiments, the lock assembly 800 can be the example rotary lockassembly 260 of FIGS. 2-6 . The lock assembly 800 includes an epicyclicgear assembly such as the example epicyclic gear subassembly 212 b.

A sun gear 840 (e.g., the example sun gear assembly 230) of theepicyclic gear arrangement may provide the mechanical drive input to thegear assembly, and a planet carrier 852 couples a screw lead (e.g., thescrew lead 282) to a planet gear 844 to provide the energy to extend andretract the linear output assembly 206. An outer diameter of the ringgear 848 (annulus, shown in FIGS. 9 and 10 ) of the epicyclic geararrangement may be nested in a bearing race and directly attached to alock rotor 816 visible in FIG. 11 (e.g., the lock rotor 270) via a rotorextension 856. In operation, the ball screw serves as the driver, andthe linear output member is responsive to the rotation of the ball screwto move axially.

In an exemplary embodiment, rotation of the lock rotor 816 to move tothe unlocked position may be provided by the epicyclic gear assemblyinitially operating in what is known as a “star” mode, during a lostmotion stroke. With reference to FIG. 9 , the rotor extension 856 (whichis coupled to ring gear 848) acts as a key that engages a radial slot860 that defines the rotational end stops of the lock rotor 816 from thelocked to unlocked position. In some embodiments, a torsion spring maybe included that directly biases the lock rotor 816 to the lockedposition.

In use, to extend the linear output assembly 206, energy is input (suchas via a motor, for example) to the sun gear assembly 230. Because thelinear output assembly 206 is constrained from any axial motion ormovement or motion by a collection of lock keys 820 (e.g., the lock keys262), the screw lead 282 cannot turn and advance the linear outputassembly 206. Therefore, the planet carrier 852 is locked until the lostmotion unlocks the lock keys 820. As such, the only response to therotation input by the sun gear 840 is to rotate the ring gear 848, whichis coupled to the lock rotor 816. The unlocking of the lock keys 820 inresponse to rotation of the lock rotor 816 mechanically coincides withthe rotor extension 856 bottoming out in the slot 860. Bottoming out ofthe rotor extension 856 in the slot 860, and unlocking the lock keys820, thereby results in locking the ring gear 848 and freeing the planetcarrier 852 to allow a planet gear 844 to revolve around the sun gear840. Thus, the epicyclic gear arrangement changes from star mode (fixedplanet carrier 852, free sun gear 840, and free annulus 848) toplanetary mode (fixed annulus 848, free sun gear 840, and free planetcarrier 852). In the planetary mode, the energy input to the sun gear840 is used to cause the planet gear 844 to revolve around the sun gear840, and drive the planet carrier 852, which, in turn drives the screwlead 282 and thereby, via nut 284, causes the linear output assembly 206to move axially.

To retract the linear output assembly 206 and rotate the lock rotor 816to the locked position, this process is reversed. The motor driving thesun gear 840 reverses direction. The ring gear 848 reverses the loaddirection and attempts to rotate the lock rotor 816 from the unlockedposition to the locked position. However, the lock keys 820 areconstrained in the withdrawn position within the grooves 838 of the lockrotor 816 by the lock key retainer 290, and thereby prevent any rotationof the lock rotor 816. This effectively locks the ring gear 848 (e.g.,via rotor extensions 856), and defines the epicyclic mode. Therefore,the input rotation of the sun gear 840 is transferred to the planetcarrier 852, which causes the screw lead 282 to rotate, and retract thelinear output assembly 206.

In response to the linear output assembly 206 coming to the fullyretracted position, the lock key retainer 290 is pushed out of the way(axially) by the linear output assembly 206 and the lock keys 820 arealigned with the groove 264 in the linear output assembly 206. Inresponse to the linear output assembly 206 being fully retracted, andthus no longer capable of any further axial motion, the screw lead 282(and thus planet carrier 852) is locked, and the epicyclic geararrangement transitions from planetary mode to star mode. This nowallows the lock rotor 816 to rotate from the unlocked to the lockedposition, pushing the lock keys 820 radially inward into the groove 264,thus re-locking the linear output assembly 206.

It will be appreciated that the output rotation direction of the ringgear 848 and lock rotor 816 during the lost motion stroke (e.g., starmode) is opposite of that of the planet carrier 852 and the screw lead282 during extension of the linear output assembly 206 (e.g., planetarymode). This is a fundamental characteristic of epicyclic gears operatedin both star and planetary modes. This lost motion feature results in adesign that is self-locking and self-unlocking without any additionalcommands or signals required in addition to the drive torque.

To increase clarity, additional cross sectional figures of the lockassembly 800 as described herein and shown in FIG. 8 are provided. FIG.9 depicts a cross section view of the epicyclic arrangement shown inFIG. 8 including the sun gear 840, planet gear 844, ring gear 848, andplanet carrier 852. FIG. 10 depicts a cross section view of theepicyclic arrangement shown in FIG. 8 including the ring gear 848,planet carrier 852, and rotor extension 856. FIG. 11 depicts a crosssection view of the lock rotor 816 with lock keys 820 in the lockedposition.

As shown in FIG. 11 , the lock rotor 816 is disposed coaxially with thelinear output assembly 206, and includes a bore 828 having an innersurface 817 that interfaces with a crown 832 of the lock key 820. A lockring 836 is grounded (e.g., fixed relative to the housing) and includesgrooves 838 that guide the lock keys 820 and restrict their displacementto radial motion. In an exemplary embodiment, an inside radius of thebore 828 will be approximately equal to an outside radius of the crown832 when the lock key 820 is engaged with the radial groove 824. In use,in response to the lock rotor 816 being disposed in the locked positionof FIGS. 2 and 3 , the bore 828 interfaces with the crown 832 of thelock key 820 and the lock key 820 is restrained from any outward radialmotion (such as the lock key motion illustrated in FIG. 4 , forexample). Therefore, the lock key 820 engages and is retained or heldwithin, the groove 824 of the linear output assembly 206 by the rotationof the rotary input shaft member 204.

FIG. 12 shows a flow diagram of an example process 1200 for operating alinear actuator. In some implementations, the process 1200 can beperformed by all or part of the example linear actuator 100 of FIG. 1and/or the example locking rotary actuator mechanism 200 of FIGS. 2-6 .

At 1210, torque is received at a first sun gear of a first epicyclicgear assembly. For example torque from the rotary input shaft member 204can be received at the sun gear assembly 220.

At 1220, torque is transmitted from the first sun gear to a first ringgear of the first epicyclic gear assembly through a first planet gearassembly of the first epicyclic gear assembly. For example, torque canbe transmitted from the sun gear assembly 220 to the ring gear assembly222 through the planet gear assembly 224.

At 1230, torque is transmitted from the first planet gear assembly to ascrew. For example, rotation of the planet gear assembly 224 can urgerotation of the screw lead 282 through the planet carrier 225.

At 1240, movement of a linear output member is urged through a nutconfigured for linear motion based on rotation of the screw. Forexample, rotation of the screw lead 282 relative to the nut 284 can urgelinear movement of the linear output assembly 206.

1250, torque is transmitted from the first ring gear to a second sungear of a second epicyclic gear assembly. For example, rotation of thering gear assembly 222 can urge rotation of the sun gear assembly 230.

At 1260, torque is transmitted from the second sun gear to a secondplanet gear engaged between the second sun gear and a second ring gear.For example, torque applied to the sun gear assembly 230 can betransmitted to the planet gear assembly 234, which is engaged betweenthe sun gear assembly 230 and the ring gear assembly 232.

In some implementations, the process 1200 can also include urging radialdisplacement of a lock key from a first lock key configuration to asecond lock key configuration based on linear movement of the linearoutput member. For example, the lock rotor 270 can be moved from alocked rotational position to an unlocked rotational position, which canallow the lock keys 262 to move radially outward from a lockedconfiguration to an unlocked configuration.

In some implementations, the process 1200 can also include contacting,based on movement of the linear actuator, the lock key with an axialgroove face of a groove defined in the linear output member andconfigured to receive the lock key in the first lock key configuration.In the first configuration, the lock key can prevent linear movement ofthe linear output member based on mechanical interference between thelock key and the axial groove face, and can prevent rotation the screwbased on the prevented linear movement of the linear output member. Withrotation of the screw prevented, rotation of the first planet gearassembly is also prevented based on the prevented rotation of the screw,which can cause substantially all torque received at the first sun gearto be transmitted to the first ring gear. For example, the linear outputassembly 206 can contact the lock keys 262 in the groove 264 to preventfurther axial movement of the linear output assembly 206. With movementof the linear output assembly 206 stopped, rotation of the screw lead282, the sun gear assembly 230, and the planet carrier 225 is stopped.With the planet carrier 225 prevented from moving, substantially alltorque from the sun gear assembly 220 is transmitted to the ring gearassembly 222.

In some implementations, the process 1200 can also include transmittingtorque from the second planet gear to a lock rotor, and rotating thelock rotor from a first lock rotor configuration to a second lock rotorconfiguration. For example, movement of the planet gear assembly 234 canbe transmitted to the lock rotor 270 through the planet carrier 235.

In some implementations, the first lock rotor configuration can be afirst rotational position defined by a first lock rotor end stopconfigured to mechanically interfere with rotation of the lock rotor ina first direction, and the second lock rotor configuration is a secondrotational position defined by a second lock rotor end stop configuredto mechanically interfere with rotation of the lock rotor in a seconddirection opposite the first direction. For example, the example radialslot 860 can defines the rotational end stops of the lock rotor 816 fromthe locked to unlocked position.

In some implementations, the lock rotor can be configured to preventradial displacement of a lock key from a first key configuration to asecond key configuration in the first lock rotor configuration, and isconfigured to permit radial displacement of the lock key from the firstkey configuration to the second key configuration in the second lockrotor configuration. For example, FIG. 11 shows that the lock rotor 816includes grooves 838 that guide the lock keys 820 and restrict theirdisplacement to radial motion. In response to the lock rotor 816 beingdisposed in the locked position of FIGS. 2 and 3, the bore 828 caninterface with the crown 832 of the lock key 820 and the lock key 820can be restrained from any outward radial motion (such as the lock keymotion illustrated in FIG. 4 , for example). Therefore, the lock key 820engages and is retained or held within, the groove 824 of the linearoutput assembly 206 by the rotation of the rotary input shaft member204. When the lock rotor 816 is rotated to bring the grooves 838 intoradial alignment with the crowns 832, the lock keys 820 have sufficientspace to move radially outward, out of contact with (and thus unlocking)the linear output assembly 206.

Although a few implementations have been described in detail above,other modifications are possible. For example, the logic flows depictedin the figures do not require the particular order shown, or sequentialorder, to achieve desirable results. In addition, other steps may beprovided, or steps may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

1-8. (canceled)
 9. A method of locking a linear actuator, the methodcomprising: receiving torque at a first sun gear of a first epicyclicgear assembly; transmitting torque from the first sun gear to a firstring gear of the first epicyclic gear assembly through a first planetgear assembly of the first epicyclic gear assembly; transmitting torquefrom the first planet gear assembly to a screw; urging movement of alinear output member through a nut configured for linear motion based onrotation of the screw; transmitting torque from the first ring gear to asecond sun gear of a second epicyclic gear assembly; and transmittingtorque from the second sun gear to a second planet gear engaged betweenthe second sun gear and a second ring gear.
 10. The method of claim 9,further comprising urging radial displacement of a lock key from a firstlock key configuration to a second lock key configuration based onlinear movement of the linear output member.
 11. The method of claim 10,further comprising: contacting, based on movement of the linearactuator, the lock key with an axial groove face of a groove defined inthe linear output member and configured to receive the lock key in thefirst lock key configuration; preventing linear movement of the linearoutput member based on interference between the lock key and the axialgroove face; preventing rotation the screw based on the prevented linearmovement of the linear output member; preventing rotation of the firstplanet gear assembly based on the prevented rotation of the screw; andtransmitting substantially all torque received at the first sun gear tothe first ring gear.
 12. The method of claim 9, further comprising:transmitting torque from the second planet gear to a lock rotor; androtating the lock rotor from a first lock rotor configuration to asecond lock rotor configuration.
 13. The method of claim 12, wherein thefirst lock rotor configuration is a first rotational position defined bya first lock rotor end stop configured to interfere with rotation of thelock rotor in a first direction, and the second lock rotor configurationis a second rotational position defined by a second lock rotor end stopconfigured to interfere with rotation of the lock rotor in a seconddirection opposite the first direction.
 14. The method of claim 12,wherein the lock rotor is configured to prevent radial displacement of alock key from a first key configuration to a second key configuration inthe first lock rotor configuration, and is configured to permit radialdisplacement of the lock key from the first key configuration to thesecond key configuration in the second lock rotor configuration. 15-22.(canceled)